In U.S. Pat. No. 4,683,039, assigned to Sterling Canada, Inc. and the disclosure of which is incorporated herein by reference, there is described the production of chlorine dioxide and its separation using gas membranes, i.e. microporous hydrophobic membranes which permit gas or vapor of chlorine dioxide to pass therethrough but resist the passage of liquid and ions therethrough.
U.S. Pat. No. 2,163,793 describes an electrochemical chlorine dioxide generating process in which a mixture of alkali metal chlorite and alkali metal chloride is electrolyzed in an electrolytic cell equipped with a porous diaphragm separating the anode and the cathode compartments.
British Patent No. 714,828 describes a process for the production of chlorine dioxide by electrolysing an aqueous solution containing chlorite and a water soluble salt of an inorganic oxy-acid other than sulfuric acid while U.S. Pat. No. 2,717,237 discloses a method for producing chlorine dioxide by electrolysis of chlorite in the presence of sulfate ions.
Japanese Patent Publication No. 81-158883, published Dec. 7, 1981, describes an electrolytic process for producing chlorine dioxide by electrolysis of chlorite in which the electrolysed solution, at a pH of 2 or less, is fed to a stripping tank where air is introduced to recover the chlorine dioxide.
U.S. Pat. No. 4,542,008 describes an electrolytic process for chlorine dioxide production in which the sodium chlorite concentration in the anolyte is monitored and controlled by means of a photometric cell.
Published International patent application WO 91/09158 discloses a method of producing chlorine dioxide from chlorite in an ion exchange compartment of a multi-compartment cell in which hydrogen ions generated in the anode compartment enter the ion exchange compartment through a cation exchange membrane, causing chlorite ions decomposition to form chlorine dioxide and other by-products.
Published International patent application WO 91/09990 teaches an electrochemical process for producing chlorine dioxide from dilute alkali metal chlorite solution in a single pass mode using a porous flow-through anode in which the unconverted chlorite together with other components of the anolyte constitute an effluent.
A disadvantage of all of the above described electrolytic processes for the production of chlorine dioxide is that they are not suitable for a highly efficient, continuous, effluent-free operation in which all the components of the chlorite feed are safely and very efficiently removed with formation of an essentially pure chlorine dioxide, whereby no undesired or harmful by-products or contaminants are generated or accumulated.